In recent years, a type of mobile communications network known as an ad-hoc network has been developed. An ad-hoc network typically includes a number of geographically-distributed, potentially mobile units, sometimes referred to as “nodes,” which are wirelessly connected to each other by one or more links (e.g., radio frequency communication channels). In this type of network, each mobile node is capable of operating as a base station or router for the other mobile nodes, thus eliminating the need for a fixed infrastructure of base stations.
A wireless mesh network is a collection of wireless nodes or devices organized in a decentralized manner to provide range extension by allowing nodes to be reached across multiple hops. In a multi-hop network, communication packets sent by a source node can be relayed through one or more intermediary nodes before reaching a destination node. A large network can be realized using Mesh Point Roots (MPR) which provide wireless nodes with access to a wired backhaul. A mesh network therefore typically comprises one or more Mesh Point Roots (MPR), and a number of Mesh Points including Routers and Mobile Nodes. Routers provide data service to mobile nodes. A Router can connect to a MPR directly or through a multi-hop route. More sophisticated ad-hoc networks are also being developed which, in addition to enabling mobile nodes to communicate with each other as in a conventional ad-hoc network, further enable the mobile nodes to access a fixed network and thus communicate with other mobile nodes, such as those on the public switched telephone network (PSTN), and on other networks such as the Internet.
Typically, in a mesh network a MPR communicates with the Mesh Points (routers and mobile nodes) by transmitting and receiving packets on radio channels. In certain cases, the MPR switches the channel on which it is communicating with the MPs. For example, the MPR switches its channel when it detects a Radar signal on the channel. If during operation, a MPR detects a radar event over the Radio Frequency (RF) channel that the network backhaul uses, it must immediately change to another available radio frequency (RF) channel. This is dictated by Federal Communications Commission (FCC) and European Telecommunications Standards Institute (ETSI) standards, and is established to allow the sharing of the five Gigahertz (5 GHz) spectrum between wireless LAN (WLAN) and military or weather radars that use the same frequencies. Alternatively, the MPR can switch channel if it detects a need for a periodic scan, or if it detects a weak radio link with the MPs.
In some traditional mesh systems, it takes significant amount of time for a MP to detect the loss of a MPR when the MPR switches its channel of operation. Conventionally, a MP will detect a lost connection with a MPR after missing infrastructure hello frames or by timing out. Also, additional time is spent by the MP in scanning for new channels and then associating with the same or a new MPR. Generally, during the transition period of the channel switch operation at the MPR, associated MPs are unable to provide meshing services to their clients.
A recent amendment to the Institute of Electrical and Electronics Engineers (IEEE) 802.11n standard provides the flexibility for a router and/or a station (STA)/mobile node (MN) to operate in either 20 or 20/40 Megahertz (MHz) channels. (For this and any IEEE standards recited herein, see: http://standards.ieee.org/getieee802/index.html or contact the IEEE at IEEE, 445 Hoes Lane, PO Box 1331, Piscataway, N.J. 08855-1331, USA.) Devices operating in 20/40 MHz bandwidth can dynamically transmit in either 20 or 40 MHz channels (depending on clear channel assessment). In this situation, one of these channels is identified as the primary channel and it is essential for a MP to have its primary channel free of radar signals to operate. As discussed previously herein, when a MP detects a radar signal in its primary channel, it will cease its operation within the Channel Move Time and for the Non-Occupancy Period. After radar's presence is detected, all transmissions shall cease on the operating channel within 10 seconds, which is the value of channel move time. The aggregate duration of all transmissions on this channel during the channel move time shall be limited to 260 milliseconds (ms) which is the value of Channel Closing Transmission Time. See, for example, European Telecommunications Standards Institute (ETSI) Digital Mobile Radio (DMR) specification (ETSI EN 301 893). Any of the ETSI standards or specifications referred to herein may be obtained at http://www.etsi.org/WebSite/Standards/Standard.aspx or by contacting ETSI at ETSI Secretariat, 650, route des Lucioles, 06921 Sophia-Antipolis Cedex, FRANCE.
In addition, intermittent management and control signals can be sent during the remaining time to facilitate vacating the operating channel. A channel that has been flagged as containing a radar system, either by a channel availability check or in-service monitoring, is subject to a non-occupancy period of at least 30 minutes. The non-occupancy period starts at the time when the radar system is detected. In general, the ceasing of operation by the MP as required will result in communications service disruption for the subscriber stations (STAs)/mobile nodes that depend upon the MP.
One disadvantage of the router ceasing operation is that even if the secondary channel is available and free of radar signals, the router will cease its operation for the Non-Occupancy Period, until its primary channel becomes free. This issue may become more severe for IEEE 802.11 VHT (Very High Throughput) which is suggesting 80 MHz operation.
Accordingly, there is a need for a method for communicating primary and secondary channel communication information within a wireless communication system.
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The apparatus and method components have been represented where appropriate by conventional symbols in the drawings, showing only those specific details that are pertinent to understanding the embodiments of the present invention so as not to obscure the disclosure with details that will be readily apparent to those of ordinary skill in the art having the benefit of the description herein.